Get First & Last Name of All AD Accounts - vb.net

Question

I'm looking for the quickest and easiest way to retrieve all Active Directory account's first & last names. The intention is to have a string list which contains all names from the Active Directory, for the purpose of auto-completion in a textbox in a small Visual Basic application used for unlocking accounts.
Usage Scenario:
On form load the application generates the list of names from the AD. I'm expecting this to take around 10-15 seconds as there's 4,500 accounts on the AD. Each name is added to a string list for use with the auto completion.
The user types the name Garry into textbox1 and the auto complete suggests all Garry's in the AD, by using a string list. I know how to do this easily, I just dont know how to populate the list with user's names efficiently.
There's a lot of samples on accessing the AD, but none which show how to loop through it. I thought asking on here would help both myself and other users in a similar usage case.
The code I have so far for accessing a single account is shown below, however I need to loop through all AD accounts and retrieve their First & Last names.
Current Code to access single account:
'Domain is declared with the LDAP path
'UserName is declared with textbox1.text value
Dim ADEntry As New DirectoryServices.DirectoryEntry("LDAP://" & Domain)
Dim ADSearch As New System.DirectoryServices.DirectorySearcher(ADEntry)
ADSearch.Filter = ("(samAccountName=" & UserName & ")")
ADSearch.SearchScope = System.DirectoryServices.SearchScope.Subtree
Dim UserFound As System.DirectoryServices.SearchResult = ADSearch.FindOne()
If Not IsNothing(UserFound) Then
Log.AppendLine("Account found, loading checks...")
Dim Attrib As String = "msDS-User-Account-Control-Computed"
Dim User As System.DirectoryServices.DirectoryEntry
User = UserFound.GetDirectoryEntry()
User.RefreshCache(New String() {Attrib})
'Display user account details
txtLogin.Text = User.Properties("userPrincipalName").ToString
txtName.Text = User.Properties("givenName").ToString & " " & User.Properties("sn").ToString
else
'User not found
end if
Any help would be much appreciated, even in C#.

Answer 1

You can use the same ADEntry variable as above and do something like this. This only adds a user to the list if they have both a first and last name.
Dim listNames As New AutoCompleteStringCollection
Using ADSearch As New DirectoryServices.DirectorySearcher(ADEntry, "(&(objectCategory=person)(objectClass=user))", {"givenName", "sn"}, DirectoryServices.SearchScope.Subtree)
For Each user As DirectoryServices.SearchResult In ADSearch.FindAll
Try
listNames.Add(user.GetDirectoryEntry.Properties("givenName").Value.ToString + " " + user.GetDirectoryEntry.Properties("sn").Value.ToString)
Catch ex As Exception
End Try
Next
End Using
With TextBox1
.AutoCompleteCustomSource = listNames
.AutoCompleteMode = AutoCompleteMode.SuggestAppend
.AutoCompleteSource = AutoCompleteSource.CustomSource
End With